大同煤田8号原煤及风化煤中常量元素和稀土元素地球化学特征

Geochemistry characteristics of major and rare earth elements in No.8 raw and weathered coal from Taiyuan Formation of Datong coalfield

运用电感耦合等离子质谱、XRD、XRF等技术手段测试了大同煤田太原组8号原煤及风化煤中常量元素和稀土元素含量,分析了常量元素和稀土元素在原煤及风化煤中的地球化学特性、赋存特征和指相意义。结果表明,太原组8号煤风化后,Fe2O3受后生黄铁矿影响含量明显增高;煤层风化过程中释放的部分Si离子以及大量不稳定物质的流失造成Si O2含量相对增大;Ca,Mg离子则被迁移至夹矸和顶底板中导致含量明显降低;除个别分层中出现明显镧系收缩效应,稀土元素含量明显增高;稀土元素赋存状态由碳酸盐及有机结合态转为铝硅酸盐矿物结合态、水合磷酸盐结合态和硫化物结合态,重稀土在煤层风化前后始终表现出与碳酸盐矿物的强烈亲和性;稀土元素与铝硅酸盐矿物的相关性可能与矿物的种类有关;常量元素灰成分参数和铈异常参数值在煤层风化后对原始沉积环境的指相意义不再明确;铕异常参数值不易受风化作用影响,仍可反映煤层的原始沉积环境。

This paper presents the data on the mineral composition, major and rare earth elements and ytterbium （REY） content variation in No. 8 raw and weathered coal from the Taiyuan Formation of Datong coalfield. The optical microscope,inductive coupling plasma mass spectrum, X-ray and XRF means were applied for investigating the geochemistry, facies significance and occurrence characteristics of the major and rare earth elements. The results indicate that the content of some major elements and rare earth elements took place great changes in No. 8 weathering coal seam. Fe203 content is higher and significantly affected by deuterogenesis pyrite. SiO2 content relatively increases partly due to the release of the Si ion and partly due to the loss of volatile matter in the weathering process of coal seam. Ca and Mg contents decrease obviously due to the ions were migrated into parting, roof and floor. In addition, the individual layer behavior in the lanthanide contraction effects obviously, and the rare earth element content increases obviously. The occurrence of REY also changes to silicate bonate and organic bound. No matter whether exist the mineral, hydration-phosphate and sulfide binding from the car- weathering affection or not,the HREY always shows the strong affinity with carbonate minerals. The facies significance of ash component for major element and cerium anomaly parameters to the original sedimentary environment mean no longer precise after the weathering of coal seam. Europium anomaly is less affected by weathering and can still reflect the original sedimentary environment of the coal seam.